Technical Field
Exemplary aspects of the present disclosure generally relate to a projection optical system, and a projection apparatus including the projection optical system, and a projection system including the projection apparatus.
Related Art
A projection apparatus, which may be implemented as any type of projector, enlarges and projects an image displayed on an image display element onto a projection surface, such as a screen. Such a projection apparatus is hereinafter referred to as a “projector”.
The image display element, which is a digital micro mirror device (DMD) or any type of liquid crystal panel, allows the image to be displayed as an arrangement of pixels. The image display element has a surface referred to as an “image display surface”, on which an image is displayed.
A projection optical system forms, on the projection surface, an enlarged image of the image displayed on the image display element. As such a projection optical system, there is known a projection optical system incorporating a refractive optical system including a lens system and a reflective optical element having a power. This type of projection optical system has a reduced projection distance between a projection apparatus and a projection surface, thereby allowing projection with an ultra-short projection distance.
In typical projection apparatuses, an image enlarged and projected onto a projection surface changes in size with projection distance. In this case, focusing is performed to bring the image to be enlarged and projected onto the projection surface into focus, according to the projection distance changed.
As the focusing techniques, there has been known any type of floating focusing technique, in which the optical elements constituting a projection optical system separately displace.